Abstraction for a NXT motor. Three instances of Motor are available: Motor.A, Motor.BTo control each motor use methods forward, backward, reverseDirection, stopTo set each motor's speed, useSpeed is in degrees per second. Methods that use the tachometer: regulateSpeed, rotate, rotateTo. These rotate methods may not stop smoothly at the target angle if called when the motor is already moving Motor has 2 modes : speedRegulation and smoothAcceleration which only works if speed regulation is used. These are initially enabled. The speed is regulated by comparing the tacho count with speed times elapsed time and adjusting motor power to keep these closely matched. Smooth acceleration corrects the speed regulation to account for the acceleration time. They can be switched off/on by the methods regulateSpeed() and smoothAcceleration(). The actual maximum speed of the motor depends on battery voltage and load. With no load, the maximum is about 100 times the voltage.
Speed regulation fails if the target speed exceeds the capability of the motor. If you need the motor to hold its position and you find that still moves after stop() is called , you can use the lock() method. inner class to regulate speed; also stop motor at desired rotation angle set by smoothAcceleration, forward(),backward(), setSpeed(). Use this constructor to assign a variable of type motor connected to a particular port. Causes motor to rotate backwards. Causes motor to float. Causes motor to rotate forward. returns actualSpeed degrees per second, calculated every 100 ms; negative value means motor is rotating backward Return the angle that a Motor is rotating to. Returns the current power setting. Returns the current motor speed in degrees per second Returns the tachometer count. Returns true iff the motor is in motion. returns true when motor rotation task is not yet complete a specified angle Applies power to hold motor in current position.
turns speed regulation on/off; Cumulative speed error is within about 1 degree after initial acceleration. Resets the tachometer count to zero. Reverses direction of the motor. causes motor to rotate through angle. causes motor to rotate through angle; iff immediateReturn is true, method returns immediately and the motor stops by itself If any motor method is called before the limit is reached, the rotation is canceled. causes motor to rotate to limitAngle; Then getTachoCount should be within +- 2 degrees of the limit angle when the method returns if immediateReturn is true, method returns immediately and the motor stops by itself and getTachoCount should be within +- 2 degrees if the limit angle Sets motor speed , in degrees per second; Up to 900 is possible with 8 volts. causes run() to exit Causes motor to stop, pretty much Methods inherited from class lejos.nxt.BasicMotor isBackward, isFloating, isForward, isStopped
Methods inherited from class java.lang.Object equals, getClass, hashCode, notify, notifyAll, toString, wait, wait public static final Motor A public static final Motor B public static final Motor C « Previous • TOC • Next » This Motor class provides access to the NXT motors. To be useful, a motor must be connected to one of the three NXT motor ports. This class provides an instance for each port. They are: Motor.A, Motor.B and Motor.C. Each of these three objects is an instance of the class NXTRegulatedMotor. class provides methods for controlling the motor, and for finding out what the motor is doing. This tutorial contains a set of five programs for you to write. you can perform experiments to understand how the NXT motor performs. They are simple enough so you don’t need much Java experience (beyond loops) to writeFinally, there is a discussion of other motor methods , not used in the programs, that you might find useful.
This program uses the most basic motor methods that control movement. They are listed below, together with other methods you will need for this program. Start the motor rotating forward Wait till any button is pressed drawString(String str, int x, int y) Draw a string at position x in row y The NXT motor has a built in tachometer that keeps track of the current angle (in degrees) of the motor axle. The purpose of this experiment is to find out how quickly the motor stops. attempt to rotate the motor exactly 4 revolutions. It uses two different ideas to accomplish this goal. The first idea set the motor speed at 2 revolutions per second and stop after two seconds. The second idea is to stop the motor after 4 revolutions, as measured by the tachometer. Returns the motor angle in degrees. speed – degrees per second.. The maximum speed that can be accurately maintained is about 110 times the battery voltage. Pause the program for interval milliseconds
Observe that in the first attempt, the stop instruction is issued before the motort has quite completed the 4 revolutions in 2 seconds, and that the it does not stop immediatel because of inertia. The Motor class has a regulator thread that runs all the time. principle jobs, one of which is to stop the motor at a specified angle. This program will test the accuracy of the methods to accurately control the rotation. The methods have two versions. The basic method returns only when the rotation is complete, the other returns immediately but the motor stops when the rotation is completed. Rotates through angle degrees The motor usually stops within 1 degree of the specified angle if the motor regulator is doing its job. It works by calculating how far the motor will continue to turn after the brake has been applied and applies the brake before reaching the specified angle. Observe: Once the motor has stopped if you try to turn it by hand it will resist you and will even
return nack to the stopped position. This is because when the regulator will continue to control the motor at its stopped position. Sometimes you will want the motor stop (or do something else) before it reachesThis program will detect a button press to interrupt the rotation task if you press a button soon enough. rotate() methods will not return until the motor has stopped at theBut the new methods in this program can returnThe motor will still stop at the specified angle unless a new motor method is called in the meantime. The method returns immediately if the boolean parameter immediateReturn is true Returns false when the motor has stopped at the specified angle Observe: if you press the button before the rotation is complete, the motor will stop without completing its rotation. Otherwise, the stop() method has no The other principle task of the regulator thread is to control the motorOne reason for doing this is that a two wheel vehicle will only
travel in a straight line if both motors run at the sameThe standard Lego software solves this problem by directly synchronizing two motors. NXJ takes a different approach: keeping each motor rotation synchronized to the system clock. regulator compares the tacho count (minus its reference count) with speed times elapsed time, and adjusts the power to keep these twoThe regulator resets its reference count and its elapsed time to zero and begins its comparison again whenever you call any of the methods you have used so far. This program allows you to experiment with the effectiveness of speed regulation in keeping motors synchroniced. You will not need any new methods for this program. The motors should remain within 1 or 2 degrees of each other, once the target speed is attained. Speed regulation depends on increasing or decreasing power. But if the motor is the motor cannot acheive the desired speed even at maximum power, speed regulation is impossible.
The maximum speed for reliable reglation is approximately 100 times the battery voltage. You should repeat the experiment with target speed of 1000 deg/sec to verify this. In some robots, the motor speed should not be constant but changed in response to a sensor reading as for example in a line follower or aIf the speed corrections happen frequently, there is no advantage in the regulator thread using CPU cycles in adjusting the motor power to maintain constant speed between adjustments. To use an unregulated Motor you must create an instance of the class NXTMotor. NXTMotor m1 = new NXTMotor(MotorPort.A); NXTMotor has many of the methods of NXTRegulatedMotor, but instead of the setSpeed method, it has a setPower method, and, as it has no regulation thread, it does not support any of the rotate methods. If you specify a very slow speed, the power to maintain it may not be enough overcome the motor internal friction, so the motor never moves.
In this case, a call to rotate() will never return. regulation on, the regulator will keep increasing the power until the motor comes up to speed.Simply create an instance of both NXTRegulatedMotor and NXTMotor classes for the same motorWhen you want to use setPower simply turn off motor regulation by calling suspendRegulation on the This is useful to test if the motor has finished rotating. returns true when the Motor is moving for any reason (e.g. forward() or backward() have been called or a rotate() task is in progress) Returns the angle to which the motor is currently rotating Returns the current speed setting. Returns the actual speed of the motor. Tells you if the motor is stalled or if the regulation of the motor speed has failed (have you asked it to go faster then is possible?). This method not only sets the tacho count to 0 but also resets the origin used by the regulator thread in deciding when to stop a rotation